Tankful

Tankful adds a multiblock aquarium block. You scoop a fish into a vanilla mob bucket, click the bucket on the aquarium, and now there's an actual fish swimming around in there with the variant colors and pattern it had in the bucket.

Then you build it up, decorate it, feed the fish, knock the glass, whatever you want.

Real fish

Works with any vanilla mob bucket: cod, salmon, axolotl, pufferfish, tropical fish, tadpole. The fish keeps its variant data, so a blue axolotl stays blue, your favourite tropical fish keeps its specific stripes etc.

Right-click the aquarium with an empty water bucket to take the fish back out.

Build any shape

Place an aquarium next to another and they merge into one. The glass between them disappears, the water becomes one volume, and fish swim freely across the boundary. So you can stack them, fan them out, do a U-shape, a 27-block cube, a wall the length of your base. Whatever shape you build, the fish use all of it.

If you ever break an aquarium with fish inside, the fish redistribute into the connected neighbours instead of getting lost.

Add a floor

Right-click the aquarium with sand, gravel, or any gravity block (vanilla or modded) to give it a substrate. You'll need a floor before you can place plants or decorations on top.

There are a few non-gravity blocks that can be used as well:

Soul sand and soul soil create an upward bubble column inside the aquarium. Fish drift up through it then swim back down.
Magma block creates a downward column.

Decorate the tank

Two decoration items, both render miniaturised versions of the actual vanilla underwater structures:

Shipwreck Decoration drops a small wrecked ship inside the aquarium. Picks one of the real shipwreck variants when placed (with mast, sideways, full hull, broken halves, all that).
Ocean Ruin Decoration drops a small underwater stone ruin. Pulls from the actual cracked / mossy / brick / warm-stone pieces.

Both turn up in the matching vanilla loot chests when you go exploring shipwrecks and ruins.

You can also place anything in the tankful:plants block tag on the substrate. Kelp, seagrass, and the coral plants by default. Datapacks can extend that.

(Both plants and decorations need a floor first.)

Feeding (purely cosmetic)

Craft fish food (recipe below), right-click an aquarium, and a few drifting orange motes fall in. The fish notice them and swim over to eat.

It doesn't do anything mechanical. It's just nice to watch.

The fish spread out across multiple food drops naturally rather than dogpiling the first one. If there are more fish than motes, the leftovers just keep wandering instead of crowding around something they can't eat.

Knock the glass

Left-click an aquarium and you get the glass-tap sound and the fish near your click point scatter for a second or two. Pufferfish puff up.

Anything that hits the aquarium counts. Snowballs from a dispenser, arrows, eggs, thrown tridents. So you can build dispenser-driven fish-scaring contraptions lol.

You can still mine the aquarium normally if you hold the click in survival, the knock is just a side effect.

Fish dance to jukebox music

Place a jukebox near your aquarium and play any music disc. The fish stop wandering and start dancing in place. Each fish picks one of a few different dance styles based on its UUID, so a school doesn't all do the same move at once.

Stop the music and they go back to swimming.

Showcase mode

Wire a redstone signal into an aquarium and the whole connected aquarium switches into showcase mode. The water gets a little more opaque, the floor and decorations and plants pop visually, the fish swim faster, and bubble effects pick up.

Signal strength scales the effect. Faint signal, actually darker than default. Full strength, full lit-up display.

A comparator on the side reads the fish count in that cell, capped at 15. Useful for auto-feeders or empty-aquarium alerts.

It looks great in your hand

The aquarium item renders with its actual contents in the hotbar, your hand, the inventory, and item frames. So if you pick up a captured aquarium with an axolotl inside, you can watch the axolotl swim around in the held cube. Same for ground item drops.

Aquariums remember what's inside them

Silk-touch an aquarium and the dropped item carries every fish, plant, and decoration that was inside. Hover over it in your inventory and you'll see a list of contents. Place it back anywhere and the contents come back.

Creative ctrl-pick works the same way. And sneak + break in creative cleanly deletes the aquarium with no item drops or stray fish entities flying out, for when you just want it gone.

Dispenser automation

Dispensers facing an aquarium do useful things:

Loaded with fish food: sprinkles food into the aquarium.
Loaded with a mob bucket: releases the fish into the aquarium, replaces the dispenser slot with an empty water bucket (so a hopper-fed loop can re-stock it).
Loaded with a water bucket: extracts the nearest fish from the aquarium as a filled bucket.

Build a closed bucket-cycling loop for automated stocking, or pair a comparator with a fish-food dispenser for an auto-feeder.

Buy from a fisherman

A master-tier fisherman villager will trade 6 emeralds for 4 aquariums, so if you've got an emerald farm but no glass farm there's a path.

The shipwreck and ocean ruin decorations also drop in matching vanilla loot chests, no need to craft.

Recipes

Item	How
Aquarium ×8	8 glass around 1 water bucket. Bucket comes back.
Fish food ×8	1 raw salmon, 1 kelp, 1 bone meal. Shapeless.

Compatibility


Minecraft	1.21.11
Loader	Fabric (0.16+)
Required	Fabric API
Optional	Mod Menu (in-game config screen)

Plays nicely with other Fabric mods. No known conflicts so far!

Configurable

Open the Mod Menu config screen, or edit config/tankful.json directly:

Max fish per cell (default 16)
Max plants per cell (default 8)
Wander speed
Food motes per click
Food mote lifetime
A few others

Translated

29 locales out of the box, including most major spoken languages plus a couple of vanilla-style fun ones (LOLCAT, Pirate Speak). Auto-translation quality, so native speakers please flag corrections in the comments.

Issues / suggestions

Bugs and feature requests, drop them in the comments below.